The invention relates to a pair of scissors, in particular hair-cutting scissors, with a hinged joint consisting of a hinge screw and a screw nut, where the hinge screw is essentially non-rotatably connected to one scissors half and the screw nut engages in a bore in this scissors half, in which a first flexible body is situated which, under contact pressure, sits against the end of the screw nut facing the head of the hinge screw and against the shaft of the hinge screw.
A pair of scissors of this kind is known from EP 0515830 A1. In these scissors, the screw nut of the hinged joint is made of steel or another material and its inner wall displays an annular groove in which a second annular body, made of a flexible material, is located, the inside diameter of which is smaller than the thread diameter of the hinge screw. As a result of the combination of this first flexible body, inserted in the bore for the screw nut and the second flexible body located on the inner wall of the screw nut, both of which sit against the shaft of the hinge screw under contact pressure, any clearance between the hinge screw and the scissors half displaying the screw nutxe2x80x94the upper scissor bladexe2x80x94is avoided for the following reasons.
Although the hinge screw is essentially non-rotatably connected to the upper scissor blade by two opposing milled surfaces and a correspondingly shaped opening in the upper scissors half, some play of the hinge screw in the opening in the upper scissors half cannot be entirely avoided during mass production of scissors of this kind for manufacturing reasons. In today""s precision scissors with a very low closing pressure, this play manifests itself in the form of slight jerks during use of the scissors, this being perceived as unpleasant by the person using the scissors, such as the hairdresser. Moreover, the hinge screw is subject to greater wear as a result of this jerking effect. It has been found that, particularly in the case of scissors with a low closing pressure, the two flexible bodies provided pursuant to EP 0515830 A1 are perfectly sufficient for avoiding the production-related play between the hinge screw and the upper scissor blade, in that the two flexible bodies sit against both the shaft of the hinge screw and against the upper scissor blade, or the screw nut fixed on it, under contact pressure and thus establish an adequate frictional connection between the hinge screw and the upper scissor blade.
However, the solution known from EP 0515830 A1 has the drawback that, in the case of short screw nuts, the annular groove formed on the inner wall to accommodate the annular flexible body greatly reduces the thread length of the screw nut, meaning that retention of the screw nut in the upper scissor blade may be impaired under certain circumstances. As it is most important to have a tight fit which does not loosen, and also accurate, sensitive adjustment of the screw nut in order to obtain the desired closing pressure of the scissors, the screw nut must have a sufficiently long internal thread.
The present invention is therefore based on the task of further developing a pair of scissors of the type mentioned at the start in such a way that, even in the case of relatively short screw nuts, reliable retention and accurate adjustment of the same in the upper blade of the scissors are guaranteed, while preserving the advantages of the scissors known from EP 0515830 A1.
According to the invention, this task is solved in that the screw nut of a pair of scissors of the type mentioned at the start displays a groove around its circumference, in which a second flexible body is located which sits against the screw nut and the bore in the scissors half under contact pressure.
The invention makes use of a frictional connection between the hinge screw and the upper blade of the scissors. In contrast to EP 0515830, this connection does not run via the first flexible body to the upper scissor blade and via the second flexible body to the screw nut, but via the first flexible body and via the screw nut and the second flexible body to the upper scissor blade. It has surprisingly been found that, in order to solve the task, it is perfectly sufficient for the first flexible body to sit against the shaft of the hinge screw under contact pressure. The desired frictional connection between the screw shaft and the upper scissor blade, and also the targeted good fit of the screw nut thread even with a short nut, and the sensitive adjustment for setting the closing pressure, are achieved by the full length of the nut being used for the thread in order to position the nut in the upper scissor blade in non-positive fashion by the first flexible body, on the one hand, and by the second flexible body, on the other.
In particular, the invention permits a screw nut which can be located entirely, or almost entirely, within the upper scissor blade and whose end facing away from the head of the hinge screw is positioned essentially flush with the upper side of the corresponding scissors half. A pair of scissors designed in this way has the advantage that the hair cannot become entangled, as usually happens with a projecting screw, and that the hairdresser can easily cut along the comb as a result.
Although a screw nut with a neck is known from EP 0515830 A1, on the circumference of which a flexible O-ring is inserted in a corresponding annular groove, this flexible O-ring is merely intended as an alternative to the first flexible body inserted in the hinge bore in the upper scissor blade, and likewise only in combination with the flexible O-ring located on the inner wall of the screw nut. It is not suitable for solving the task on which the present invention is based, either in this combination or in isolation. The combination of two flexible bodies in accordance with the invention contradicts the theory of EP 0515830 A1, as this bindingly prescribes the use of one of the flexible bodies on the inner wall of the screw nut in both of the alternatives described.
DE 81 37 176 U1 shows a screw nut with a flexible body located in an annular groove on the circumference, said body being seated against the screw nut and the bore in the scissors half under contact pressure. However, there is no provision for a flexible body located between the shaft of the hinge screw and the upper scissor blade or the screw nut. Consequently, this design is incapable of avoiding production-related play between the hinge screw and the upper blade of the scissors, the result being that the disadvantages eliminated by DE 81 37 176 U1 and the present invention appear, that is to say jerking during professional use of scissors of this kind with a very low closing pressure and elevated wear.
In a preferred configuration of the invention, the groove located on the circumference of the screw nut is designed as an annular groove, and the second flexible body seated therein is designed in an O-ring.
In order to increase the contact pressure under which the first flexible body sits against the hinge screw, the inside diameter of the same can be designed smaller than the thread diameter of the hinge screw.
The bore serving to engage the screw nut preferably displays a narrow area at the end facing the other scissors half, where the first flexible body sits against this narrow area. In particular, the cross-section of the narrow area can essentially correspond to the cross-section of the shaft of the joint screw in order to achieve essentially non-rotatable mounting of the joint screw. In this context, the first flexible body is preferably designed as a moulded part with spatial dimensions corresponding to the geometry of the narrow area.
In a further expedient configuration of the invention, the narrow area and, accordingly, the second flexible body are of conical design.
A preferred practical example of the invention is described in more detail below on the basis of the drawings. The drawings show the following: